Rice bran forms 8-10% of the total weight of rough rice and contains approximately 90% of its nutrients and nutraceuticals. This makes rice bran a prime candidate for processing that increases the production of its valuable components. The U.S. food industry can remain competitive in a global economy by developing, from inexpensive and underutilized resources, value-added functional foods/ingredients having health benefits and consumer acceptability. The nutraceutical and functional food industry has evolved into a market worth $20.2 billion in 2002. It is estimated that the functional food industry in the U.S. could double in value by 2007 [Market Research, 2002].
Commercially, rice bran is stabilized by heat treatment to prevent deterioration resulting from hydrolysis and oxidation of oil. The commercial rice bran product after heat treatment and removal of oil (15-20%) is referred to herein as “heat-stabilized, defatted rice bran” (HDRB), and is mainly used for animal feed and pet foods. Heat treatment results in protein denaturation and aggregation with other components, and lowers protein and phytochemical extractability. HDRB contains approximately 10.5-12.0% water, 18.5-20.9% protein, 1.5-2.0% lipid, 15.3-16.8% starch, 25.2-25.6% total fiber, 2.0-2.5% total phenolics, 1.73-2.28% phytic acid, and 9.0-10.4% ash [Hettiarachchy, 2003]. In addition, rice bran contains B-vitamins and minerals, and trace elements. The positive nutritional and nutraceutical attributes of rice bran include hypoallergenicity, gluten-free, and a source of dietary fiber.
Prebiotic.
The term “prebiotic” is used to refer to a “non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health” [Gibson, et al.]. Resident gut microflora ferment prebiotics, mainly provided in the diet, which generally cannot be digested by the host in the upper part of the digestive tract. These include non-starch polysaccharides (dietary fiber), oligosaccharides, oligopeptides, etc. The resistant oligo products in the digestive tract can be utilized as substrates for the growth and/or activity of beneficial bacteria, e.g., Bifidobacterium spp. and Lactobacillus spp.
Probiotic/Synbiotic.
A “probiotic” is a live microbial organism that is beneficial to health. The combination of a probiotic and a prebiotic is called a “synbiotic”. The interaction of probiotics and prebiotics (synbiotics) has not been researched in detail. Prebiotics ensure the survivability of some beneficial bacteria, especially Bifidus bacteria. Synbiotics are generally more stable because a true probiotic, in the absence of a prebiotic, is often not very viable. Without a specific synbiotic food source, a probiotic has to deal with a greater propensity for oxygen intolerance, low pH intolerance, and temperature intolerance. Also, it is believed that the beneficial activity of probiotics requires specific prebiotic substrates for effective performance.
Exemplary food grade and generally regarded as safe (GRAS) probiotics include Lactobacilli (Lactobacillus acidophilus, L. casei, L. delbrueckii subsp bulgaris, L. brevis, L. cellobiosus, L. curvatus, L. fermentum, L. plantarum, L. gasseri, L. rhamnosus), Gram positive cocci (Lactococcus lactis subsp cremoris, Streptococcus salivarius subsp thermophillus, Enterococcus faecium, S. diacetylactis, S. intermedius), Bifidobacteria (Bifidobacterium bifidum, B. adolescentis, B. animalis, B. infantis, B. longum and B. thermophilum) and Yeasts (Saccharomyces boulardi, S. cerevisiae and other strains). This also includes the genetically modified recombinant strains of S. cerevisiae (ATCC 13007, YPG-G, ATCC 4126, YPG/AB, YPG/MM, ATCC 201160), which have potential protease and carbohydrase, esterase activities.
Probiotic bifidobacteria plays an important role in human health as indicated by suppression of liver tumorigenesis in mice [Mitzutani, et al], cholesterol reduction [Moleder, et al.], improvement of lactose utilization in malabsorbers [Jiang, et al.], deconjugation of bile acids [Lankaputhra, et al.] and increasing immunity in host animals [Simone, et al.]. Consumption of foodstuffs that promote the growth and/or activity of intestinal Bifidobacteria accordingly can enhance the health of the host.
Studies in several experimental models have shown consistently that synbiotics added to the diet of animals can dramatically reduce the development of cancer. Synbiotic combinations reportedly are more potent than either their prebiotic or probiotic components when tested alone [Rowland, et al.].
Bioactive Anti-Angiogenic Proteins.
Many well-established bioactive proteins have demonstrated anti-angiogenic activity and cholesterol-lowering effects [S. Li, et al.]. Reported anti-angiogenic bioactive proteins include protamine [Y. Li, et al.], the Bowman-Birk inhibitor (BBI) from rice, soybean and legumes [Kennedy], lactoferrin [Norrby, et al.], and lysozyme [Yamamoto, et al.].
Bioactive Anti-Mutagen Compounds.
Naturally occurring anti-mutagens and anti-carcinogens have been reported in fresh fruits and vegetables, and fermented food [Karakaya, et al.]. Glycoproteins purified from a culture supernatant of lactic acid bacteria (LAB) showed strong anti-mutagenicity [Rhee, et al.].
Bioactive Anti-Microbial Compounds.
Food-borne pathogens are a great concern to consumers and cause significant annual losses to the food industry. L. monocytogenes, S. typhymurium and E. coli 0157:H7 are among the most important pathogens that have caused a significant number of outbreaks. Frequent outbreaks demonstrate a need for development of intervention strategies using antimicrobial agents to ensure the microbial safety of food.
Bioactive Antioxidant Compounds.
Antioxidants are used in a wide variety of food products including lipids, lipid-containing foods, and packaging materials [Madhavi, et al.]. Several plant extracts have demonstrated antioxidant activities. An extract of rosemary leaves exhibited the most effective antioxidant activity among the herbs evaluated for this quality [Chang, et al.]. Cereals and legumes are rich sources of antioxidant compounds, such as phenols and derivatives, and tocols. Alpha tocopherol is the most abundant tocol in food and also the most biologically active compound [White, et al.]. However, tocopherols also have pro-oxidant effects, which limit their use in product applications. The flavor and color in plant antioxidant extracts contribute to limited usage. Antioxidant activities have been demonstrated in cereal, plant, and fenugreek extracts [Onyeneho, et al. 1991, 1993; Hettiarachchy, et al. 1996a].
Much research has been conducted on the preparation, purification, identification, and characterization of proteins from rice bran using enzymes [Hettiarachchy, et al., 1996b; Tang, 2002, Tang et al., 2002; Tang et al., 2003a, 2003b; Wang, et al.]. The nutraceutical properties and functional uses of rice bran protein for several food and pharmaceutical applications are being studied. Polyphenolic extracts and their constituents derived from selected plant materials are under investigation for antioxidant, antimicrobial, and anti-mutagenic activities [Cai, et al.].
U.S. Pat. No. 5,118,503 (issued to Sawai, et al.) proposes a composition obtained from rice bran that comprises a filtrate of lactic fermented and aged material of the rice bran. U.S. Pat. No. 5,776,756 (issued to Kimura, et al.) proposes fermentation compositions made from rice brans and soybeans, which have superoxide dismutase and anti-hypertensive activities. The fermentation composition is prepared using Bacillus microorganisms. U.S. Pat. No. 4,358,462 (issued to Takeda) proposes a method of producing an alcoholic beverage from rice that includes fermentation of a saccharified rice mash or slurry with yeast. The saccharified mash or slurry is formed by saccharifying cooked or steamed rice with an enzyme composition containing a saccharifying enzyme produced by Rhizopus, Aspergillus, Endomyces or Bacillus subtilis microorganisms.
Yeast, a unicellular eukaryotic microorganism, is used in baking, brewing, wine making, and biotechnology and is the most intensively studied organism for many biological and biochemical aspects. Many types of yeast are generally regarded as safe to human beings, which give them advantages for application in food compared to other organisms. Yeast cells have advantages for experimentation and application because of a much higher metabolic rate, a more rapid growth rate, and consequently the ability to bring about chemical changes very quickly.
It is an objective of the present invention to produce food grade yeasts or microorganisms using rice bran as an economical substrate medium. It is also an objective of the present invention to release the bound protein, phenolics and other phytochemicals from rice bran using the enzymes produced during fermentation. In rice bran more than 70% of the phenolics are in the insoluble bound form, in which they are cross-linked to carbohydrates in the cell matrix and thus are difficult to extract. Another objective of the present invention is to enhance the prebiotic and/or probiotic utilities of rice bran using yeast fermentation and probiotic processes. A further object of the present invention is to develop and identify novel nutraceuticals and health beneficial ingredients derived from rice bran by yeast, mold, microorganism and probiotic fermentations, which should increase the economic value of this commodity.